Manufacture of lactid.



. UNITED sTAT s- TEN oFFio REINIHOLD GRUTER; or CHARLOTTEhTBURG AN11'HEINBItII-I .POHL, or IBIEBItICH,'.' GERMANY, ASSIGNORS TO CHEMISCHE WERKE VORM. DR. HEINRICH BYK, or p LEHNITZ-NORDBAHN, GERMANY.

MAivUFAeTUiiE or Laotian.

No Prawing.

To all whom it may concern:

Be it known that we, REINHOLD and HEINRICIf-POHL, citizens of the German Empire, residing at Charlottenburgand Biebrich, Germany, respectively, have invented certain new and usefulImprove ments in the Manufacture of Lactid, of which the following is a specification.

Lactid is produced by heating, lactic acid.- The procedure according to Wishcenus (Ansmall, and the ultimate yield of pure lactid.

shrinksto such an extent, in consequence of the repeated recrystallization required, that the production on a commercial scale is rendered very expensive. This in'the case of lactic acid is the point which is of capi' tal importance from the point of viewof profitable commercial manufacture.

We have now found that lactid can be roduced economically and with an excel ent yield if, contrary to the directions of Wislieenus, lactic acid is first heated to a temperature above 135 C., namely to such a temperature .and for such a length of time that the lactic acid is converted into a highly molecular substance. This result is best attained by gradually heating the lactic acid to progressively higher temperatures, preferably in 'vacuo and while drawing air through. The raising of the temperature must occur so slowly that when the bath temperature has reached 150 C., the product obtained,-

contrary to that in, theWis'licenus process,

is not distillableat these temperatures. The bath temperature is then-preferably further raised for example to 200 0., the dehydration (anhydrization) proceeding still further as the result of the continued heating, and the product becoming still more highly molecular. The mass thus obtained is solid Specification of letters Patent. Application filed May 15; 1913. Serial no. 767,800.

GRtiTEi:

at ordinary temperature and owing to its highl molecular condition-1t is almost -1nsolub e in water and most organic solvents for example alcohol and ether; it dissolves however, in chloroform.

Contrary to the indications of Wislicenus the surprising fact has been found that inthe first place decomposition does not occur in the roduction of this crude product, even at the igh temperature last mentioned. It"

has further been found that this crude mass, which is but very slightly acid and is probably -to be regarded as a polylactyllactic acid, can be converted intolactid byv heating to high temperatures. This procedure at the same time represents a depolymerization. If for example this crude mass is heated to 250300 (l, the formation of lactid occurs. If one Works under reduced pressure the lactid distils over. It has been found that this process gives yields far exceeding those of Wislicenus, in fact more than double the amount. It has further been found that by adding suitable substances to the crude mass before the splitting the latter can be materially facilitated and accelerated, and with a further increase of the yield. Some substances when added have the further valuable property of substantially reducing the about 300 0., it is possible to reduce the Patented May 5, 1914.

temperature of formation of the lactid to about 200 C. by adding for instance a little zinc oxid to the crude mass. The amount of added'substance only'needs to be small. Instead of zinc oxid one can'employ aluminium oxid, magnesium .oxid and other oxide;

one can also employ hydroxids and their salts, with the exception of salts which like those of sulfuric acid have a strongly acid reaction. Thus for instance one canemploy carbonates e. g. zinc carbonate, and likewise phosphates, e. g. aluminlnum phosphate.v

Instead of the oxids the metals themselves can be used/ The addedv substances appear to act catalytically and to restrain or reduce the decomposition of the distillation mass by -means of their acid-binding property.

I vents and then at, once shows All these additions only require to be made in small quantity. In fact those of the added substances which possess a pronounced basic character, even act detrimentally on the process if employed in large quantity.

By the way described not only pure but raw commercial lactic acid can be easily converted into pure lactid, so that the present invention also provides a process of purlfying a commercial product into a pure product.

Example: Lactic acid of about '80 per cent. is heated in cacao first to 70 C. and the temperature is then progressively raised to about 200 0., the raising of the temperature being effected at such a rate that substantially only water distils over. The heat is applied until the mass obtained on cooling is quite hard and indicates only very little acid with phenolphthalein. 1 kilo of the highly molecular mass thus prepared is distilled in vacuo with 10 grams of calcined zinc oxid,'a current of carbon dioxid being preferably led through. At a bath temperature of 200220 C. 950 grams of lactid distil over and solidify in the collecting or cooling vessel. When pure acidis used the distillate ispractically free from oily constitutents. With commercial acid there is sometimes a small amount of oily substance present in the lactid, but this amount is so small that for many purposes the lactid can-be used as it is. The oil can easily be extracted by treatment with a solvent, for example a little alcohol, or ether, in which it readily dissolves. The 'distillate can be recrystallized from the known solthe rightmelt- 'ing point of above 124 C.

The slight quantity of oily substance that may be present is not destroyed material, but anhydrid acid and can be reconverted into the highly molecular product and there worked up to lactid. Even the slight residue can be utilized for which purpose it may either be further distilled at a slight increase of the temperature, or it may be converted into lactic acid or anhydrid acid and returned in this form to the process. It has in fact been found that even the residue,

A notwithstanding the high temperature employed, consists of almost indecomposed highly molecular lactic anhydrid or itssalts. Instead of zinc oxid corresponding quantitics of the other added additions mentioned can be employed, but with these, for. example with aluminium oxid,.the temperature has to .be kept about 50 higher. Instead of a current of carbon dioxid one can work with a liquid. For example by adding a hydrocarbon, which distils over, the dis-- tillationyof the lactid is facilitated. The hydrocarbon then functions as a vehicle. It is likewise possible, using such liquids to do without distillation, the lactid then goes-into the hot solvent in proportion as it forms from the raw product, and can be recovered therefrom by crystallization or evaporation. The separation of lactid and raw product in this way is possible, as only the lactid is dissolved by hot hydrocarbons and not the highl molecular raw product. The fact that lactid could be produced practically without loss and with such good yields at the high temperatures mentioned could not be foreseen, especially in view of VVislicenuss statements that the best yields are obtained not exceeding a bath temperature of 150 C.

The new process differs from that of Jungfleisch and Godchot (Centralblat 1905, I 862 and 1906, I 1329) in that it contemplates and effects a much more far-reaching anhydrization of the product to be distilled. According to J ungfleisch and Godchot the lactic acid is only heated to temperatures of about or 90 100 C. The mass thus becomes richer in lactyllactic acid, "as is distinctly stated. This product therefore, which consists mainly of lactyllactic acid, is

'not dehydrated to any great extent, but consists chiefly of anhydrid acid with free carboxyl groups. Therefore in the subsequent distillation a mixture of lactid and much lactyllated lactic acid is obtained.

We 'claim:

1. Process for the production of lactid, consisting in splitting lactic acid into a highly dehydrated product by heating at temperatures above 135 (1, and splitting this-product by further raising the tempera tures to above 200 C.

2. Process for the production of lactid, consisting in converting commercial raw lactic acid into a highly dehydrated product by heating at temperatures above 135 C., and splitting this product by further raising the temperatures to above 200 C.

3. Process for the production of lactid, consisting .in splitting lactic acid into a highly dehydrated product by heating at temperatures above 135 C., and splitting this product by further raising the tempera tures to above 200 C., and distilling in 'vacuo.

4. Process for the production of lactid, consisting in converting commercial raw lactic acid into a highly dehydrated product by heating at temperatures above 135 C., and splitting this product by further raisin the temperature to above 200 C., and distilling in c'acuo.

5. Process for the production of lactid, consisting in splitting lactic acid into a highly dehydrated product by heating at temperatures above 135 0., and splitting this product by further raising the temperatures to above 200 C. in presence of a fluid vehicle substantially as described.

.6. Process for the production of lactid,

consisting in converting commercial raw lactic acid into a highly dehydrated product by heating at temperatures above 135 0., andsfivlittlng this product byfurther raising t "e temperatures to above 200 0. in presence of a fluid vehicle substantially as described. p K 7. Process for the production of lactid, consistin in splitting lactic acid into a highly (fiih this product by furthenraisin the temperatures to above 200 0., an distilling in worm, in presence of a fluid vehicle substantially as described:

8. Process for the production of lactid,

- consisting in converting commercial raw l lytic action.

., consisting in converting commercial raw lactic acid into a highly dehydrated product by. heating at temperatures above 135 0.,

10. Process for the production of lactid,

lactic acid into a highly dehydrated product by heating at temperatures above 135 0.,

and splitting this product by further raising the temperatures to above 200 0., in. the presence of small quantities of substances having a'ca'talytic action. k

11. Process for the production of lactid, consisting in splitting lactic acid into .a highly dehydrated product by heating at temperatures above 135 0., .and splitting this product by further raising the tempera tures to above 200 0., and distilling in cacao, in the presence of small quantities of substances having a catalytic action.

12. Process forthe production of lactid,

consisting in converting commercial raw lactic acid into a highly dehydrated product by heating at temperatures. above 135 0., *and splitting this product by further raising the temperatures to above 200 0., and

- distilling in vacuo, in the presence of small quantities of substances havinga catalytic action. j 13. Process for the production'of lactid,

' consisting in splitting. lactic acid into a highly dehydrated product by ,heating at temperatures above 135 0., and splitting this product by further raising the temperatures to above 200 0., in presence of a fluid vehicle substantially as described and in the presence of small quantities or substances aving a catalyti action.

ydrated product by heating at temperatures above 135 0., and'splitting i tures to above 200 0.,

cacao, in presence of a fluid vehicle substan-- .14.'Process for the production efiiid,

consisting in converting commercial raw lactic acid into a highly dehydrated product by heating at temperatures above 135 0., and splitting this product by further raising the temperatures to above 200 0., in

presence of a fluid vehicle substantially as described and in the-presence of small quantities of substancesihaving a catalytic action.-

15. Process for the production of lactid, consisting in splitting lactic acid into a highly dehydrated product by heating at temperatures above 135 0., and splitting this product by further raising the temperaand distilling in tially' as described and inthe presence of small quantities of substances having a cata-v lytic action.-

16. Process for the production of lactid, consisting in converting commercial raw lactic acid into a highly dehydrated product by heating at temperatures above 135 0., andsplitting this product by further raising the temperatures" to above 200 0., and distilling in vacuo, in presence of af'fiuid vehicle substantially as described-and in the 1presence of small quantities of substances aving a catalytic action.

17. Process for the production of lactid, consisting in splitting lactic acid into' a, highly dehydrated product by heating at temperatures above 135. 0., and splitting this product by further raising the temperatures to above 200. 0., in the presence of small quantities of substances having an acid-binding action.

18. Process for the production of lactid,

consisting converting commercial raw lactic acid into a highly dehydrated product by heating at temperatures above 135 0., and splitting this product by further raising the temperatures to above 200 0., in the presence of small quantities ofsubstances having an acid-binding action.

19. Process for the production of lactid,

consisting in splitting lactic acid into a highly dehydrated product by heating at temperatures above 135- 0., and splitting this product by further raising the temperature to above 200 0., and distilling a. cacao, in the presence of small quantities of substances having an acid-binding action.

20. Process for the production of lactid, consisting .in. converting commercial raw lactic acidinto a highly. dehydrated product by heating at temperatures above 135 0., and splitting this product by further raising the temperatures to above 200 0., and distillingxz'n cacao, in the presence of small quantities of substances having an acid-binding action.

21. Process for the production of lactid, consistin in splitting lactic acid into a highly ehydr-ated product by heating at temperatures above 135 C, and splitting this product by further raising the temperatures to above 200 (3., in presence of a fluid vehicle substantially as described and in the presence of small quantities of substances having an acid-binding action.

22. Process for the production of lactid, consisting in converting commercial raw lacticacid into a highly dehydrated product by heating at temperatures above 135 (3., and splitting this product by further raising the temperatures to above 200 (1., in presence of afiuid vehicle substantially as described and in the presence of small substances having an acid-binding action.

23. Process for the production of lactid, consisting in splitting lactic acid into a highly dehydrated product by heating at temperatures above 135 (3., and splitting this product by further raising the temperatures to above 200 0., and distilling in cameo, in presence of a fluid vehicle substantially described and in the presence of small quantities of Witnesses asto R. Griiter: HENRY HASPER, WOLDEMAR HAU'PT.

Witnesses as to H. Pohl:

Monrrz VEZEL, v MARIE MENKE. 

